DESCRIPTION (Applicant's Abstract) : The overall goal of this renewal application is to determine the effect of simultaneous inhibition of the expression of the proliferation-associated genes dihydrofolate reductase, c-myc, and cyclin D1 in cell culture and animal models. These genes appear to play an interrelated role in the regulation of cell proliferation which is mediated through binding of E2F1 and the interaction of the myc/MAX complex with the promoters of the DHFR and cyclin D1 genes. The applicant has identified triplex-forming regions in the promoters of each of these genes. During the initial period of funding he has concentrated on the problems associated with triplex- based inhibition of specific genes. These have included: identification of biologically relevant triplex-forming sequences, oligonucleotide delivery, oligonucleotide stability, development of efficient test systems in which transcriptional inhibition can be documented, and generation of vectors for intracellular expression of triplex-forming transcripts. His extensive previous characterization of DNA binding drugs as selective inhibitors of gene expression will serve as a basis for the proposed work. It is likely that he will begin clinical trials during the proposed funding period. The specific aims of the renewal application are: 1. To test the anti-proliferative synergy of triplet-based inhibition of DHFR, c-myc, and cyclin D1 expression in malignant and normal cells in culture. 2. To develop effective delivery systems which will result in effective nuclear concentrations of triplex-forming oligonucleotides. 3. To characterize the ability to deliver effective concentrations of TFO to human tumor cells growing in nude mice. 4. To determine the ability of triplex- forming oligonucleotides targeted to the murine c-myc, cyclin D1, and DHFR promoters to inhibit the growth of murine tumors. 5. To characterize the antiproliferative effects of potential gene therapy vectors expressing putative triplex-forming transcripts targeted to the c-myc P1 and P2 promoters and the cyclin D1 promoter.